Method and apparatus for a multiple course radiobeacon



Feb. 26, 1935. H. DIAMOND 1,992,197 I I METHOD AND APPARATUS FOR A MULTIPLE COURSE RADIOBEACON Filed March 9, 152 5 Sheets-Sheet 1 FIGURE.

Feb. 26, 1935. 1,992,197

METHOD AND APPARATUS FOR A MULTIPLE COURSE RADIOBEACON H. DIAMOND Filed March 9, 1932 5 Sheets-Sheet 2 FIGURE 2 FIGURE. 3

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Feb. 26, 1935. I v DIAMOND 1,992,197

METHOD AND APPARATUS FOR A MULTIPLE COURSE BADIOBEACON Filed March 9, 1932 5 Sheets-Sheet 3 Feb. 26, 1935. H. DIAMOND 1,992,197

METHOD AND APPARATUS FOR A MULTIPLE COURSE RADIOBEAGON Filed March 9, 1952 5 Sheets-Sheet 4 BIAS VOLTAGE. J

FIGURE. 6

H. DIAMOND. 1,992,197

METHOD AND APPARATUS FOR A MULTIPLE COURSE RADIOBEACON Feb. 26, 1935.

FiledMarch 9; 1952 5 Sheets-Sheet 5 FIGURE. 7

FIGURE. 8

Patented Feb. 26, 1935 13%,1'97

V v 1,992,197 j METHOD AND APPARATUS FOR A MULTIPLE oonasr: RADIOBEACON Harry niamondjWashington, D. 0., assignor to the Government of the United States as rep-' b resented by the Secretary of Commerce 1 Application March 9, 1932, Serial No; 597,757

11 Claims. (c1. .25'o- -1'1) (Granted under the act of 'March 3, 1883, as

amended April 30, i928; 370 0. G.1757) The invention described herein may be 'manuserving twelve courses, it is to be understood that factured and used by or for the Government of a greater number of coils may be utilized to serve the United States. for governmental purposes a correspondingly greater number of courses, the without the payment of any royalty thereon. principle employed remaining the same. 7

The invention relates to methods of and ap- On the airplane, the usual indicating vibrating 5 paratus for producing directive radio beacon sigreed arrangement is used as before, but may be nals, and has fOIltS general object the provision provided withthree reeds instead of two, by of a signal transmitting apparatus capable of means of which a pilot is enabled to easily deter serving more than four courses simultaneously. mine which of the twelve courses he is on. The

. Another object is to provide means for aligning manipulation of the usual indicating apparatus 10 the radio beacon courses with the fixed airways. for the purposeris not, however, a part of the The rapid increase in the number of airways present invention, and will notbe considered in emanating from the more important airports detail. It will be described more detail has created a need for a directive radio beacon in another application for a patent. The concapableof marking outmore than 'four courses. struction and mode of operation of my invention My purpose is to render the beacon more flexible will be, more particularly understood from the and thus make it suitable for use at cities located following detailed description taken in connection 1 at the junction of a large, number of airways. To with the accompanying drawings.

accomplish this object I have developeda bea- Referrin '6 e drawings! con capable of serving-any number of courses Figurel is a diagram of a triple-modulation 20 from one to twelve simultaneously. The increase direactive radio beacon transmitter and coil anin apparatus over the beacons above described tenna system embodying my invention, in one is not great; An additional train of amplifiers particu a a m i and an additional modulating frequency are Figure2is adiagrammatic view illustrating the used, as willbe described'hereinafter. radiated beacon space pattern of the system 25 A special goniometer-is also required, having, Shown Fi ur 1 l in the preferred typefof apparatus, three stator Figure 3 is a diagrammatic V w illustrating coils, one stator coil being connected to each the corresponding polar pattern as received-On poweramplifier tube. The stator coilsin the emthe reeds. J f

bodiment of my invention are disposed at 120 gure 4 is adiagram of a triple-modulation 30 degrees to eachothenbutthese angles 'may be directive radio beacon transmitter and. coil andeviated from in any manner to obtain certain tenna system using an alternative arrangement desired conditions, as will appear hereinafter. for preventing intercoupling between amplifying The rotor system' of this goniometer comprises branches and goniometer primary coils.

two coils crossed at 90 degrees; and each 0011- Figure 5 'is a diagram showing the resultant 35 nected in series with one loop antenna. For conbiasing voltages on the grid of each intermediatevenience in goniometer'design, each rotor coil amplifier stage, 7 ismade up of three sections and each section is Figure 6 shows the space pattern radiated-by in inductive relationship with one stator. the beacon when using the grid biasing arrange- 40 Since the goniometer stator windings are not ment. for preventing intercoupling between pri- 40 at 90 degrees with each other, undesirableintermary goniometer windings. coupling between the stators will exist, unless Figure 7 shows the received pattern correcertain precautions are taken, resultingin a comsponding to the space pattern of Figure 6. binedbeacon space patternwhich can not be Figure 8 shows the displacement of beacon used. Direct inductive coupling between .stator courses obtained when shifting one stator by 20 45 windings is eliminated by the use of the sf-section degrees from its normal position. rotor system, each stator winding being placed The novel features and details embodied in my in a separate shielded compartment. invention will now be described. Referring to Indirect coupling between stator windings by Figure 1, the numeral 11 shows a conventional virtue of their mutual induction with the rotor form of master oscillator which is connected for 50 system, still exists. Methods and meansffor supplyingradio frequency in predetermined eliminating the indirect coupling will be described amounts, to the intermediate amplifier tubes 12, hereinafter. 1 l 13, leand 15. The output of the intermediate Although I shall describe thisv embodiment of amplifier 12 is modulated to, say, 65 cycles, by a my inv t usin thr co l tendoapable of. modulator 1c. .The modulated high irequency is 55 cycles, and after being amplified by a power amplifier 24, is transferred to the antennae 18 and 19 by means of the inductive relation betweena stator and the rotors 21 and 22.- Like'wisefthe output of the intermediate amplifier tube 14 is modulated by a modulator'26'to; say, 86.7 cycles,

and after amplification by a poweramplifier tube 27, is transferred to the antennae 18 and 19 by means of the inductive relation between a-stator 28 and the rotors 21 and 22. The antennae 18 and 19 are tuned to the frequency of the master oscillator by means of the 'condensers'29 and 30, respectively. The loop antenna 18 and-19 are into degrees space phaseso as to reduce the V intercoupling'to a minimum.

, Each stator coil, acting in conjunction with the two crossed-rotor coils and the two crossed loop antenna, sets up a system which is electrically equivalent to a single loop antenna. The plane of this phantom antenna coincides with the plane of the statorwinding for zero setting of the rotor, but rotates in space as the rotor system is rotated. Since there are three stator coils, placed at 120'degrees'with each other, three such. phantom antennae (crossed at 120 degrees) exist. When special precautions are taken in circuit design the combined space pattern consists of a circular carrier with three figures-of-eight sets of side bands crossed at 120 degrees.

An essential precaution is the elimination of intercoupling between the stators 20, 25 and 28,

which, if present, would result in a combinedspace pattern which can not be used. Direct inductive coupling between stator windings is eliminated by the use of the three section rotor system, each stator winding being placed in a separate shielded compartment 0:. Indirect coupling between stator windings by virtue of their mutual induction with the rotor system still exists. This coupling is somewhat more difiicult to eliminate. Several arrangements are possible for preventing this undesirable intercoupling. V 7 One arrangement consists of neutralizing this coupling by introducing inductive coupling between stator windings of opposite sense, as shown in Figure 1. Thus the stator 20 is coupledto the stator 25 by coils 31; 32; 33; 34 and to the stator 28 by coils 31; 35; 36; 37. Similarly the stator 25 is coupled to the stator 20 as noted and to the stator 28 by coils 34; 38; 39; 37. The link circuits 32,40; 33 and 35; 41; 36 and'38; 42; 39 in which 40; 41 and42 indicate variable'condensers, are each tuned to 'the'beacon carrier frequency. It is evident that by virtue of .these link circuits a current flowing in any stator induces in each of the other stators an E. M. F. 180 degrees out of phase with that current. On account of the indirect coupling between stators by way of the rotor system, a current flowing in any one stator induces in each of the other stators a voltage exactly in phase with that current. .By properly adjusting the amount of coupling due to the link circuits, an exact neutralization maybe obtained.

The carrier-frequency currents in the stators 20 ;25 and 28 have been assumed'to be in time phase. Since the stator windings are displaced by 120 degrees space phase, the resultant' carrier transmitted is zero. A circuit carrier can, however; be supplied by the use of a vertical antenna 43 extending along the beacon tower and coupled through a train of amplifying tubes to the master oscillator oi the beacon transmitting set.

The combined space pattern which consists of three figur'e-of-eight side band characteristics and a circular carrier is shown in Figure 2. 44 indicates the figure-of-eight side band characteristic from stator 20 modulated at cycles, 45 indicates a similar characteristic from the stator 25 modulated at 108.3 cycles, and 46 indicates a similar characteristic from the stator 28 modulated *at' 86.7 cycles. 47 indicates the circular carrier radiated from the vertical antenna.

The corresponding polar pattern, assuming square law detection, is'shown in Figure 3, in which 48 shows the figureof-eight reed amplitude characteristic due to the 65-cycle modulation, 49 and 50 show similar characteristics for the reed amplitudes at 86.7 and 108.3 cycles, re-

spectively. Now assume that a pilot is equipped with three vibrating-reed course indicators of the two-reed type, the first tuned to 65 and 108.3 cycles, the second to 86.7 and 108.3 cycles, and the third to 86.7 and 108.3 cycles, respectively. Using the first indicator, he will find four courses at 51; 52; 53; and 54. With the second course indicator he will observe four courses at 55; 56; 57 and 58. Similarly, with the third reed indicator, four courses at 59; 60; 61' and 62 will be obtained. Two of each set of four courses (for example, 51 and 52) have an equisignal zone of 1 to 1.5 degrees wide while the width of this zone for the other two courses, (viz. 53 and 547 is from 2 to 3 degrees.

The use of link circuits to eliminate coupling between stator windings and the need for supplying an auxiliary carrier to replace the one suppressed by the goniometer system may both be precluded if means are provided for exciting but one stator winding at a time. A circuit arrangement accomplishing this desired result is shown in Figure n Which the numeral 101 is a conventional form of master oscillator supplying radio-frequency power to the three intermediate power amplifier tubes 102; 103; and 104 at, say, 290 kc, through the medium of balancing resistors 105 andc'onductors'attached thereto. 1%; 107 and 108 denote transformers, one terminal of the secondary of each is connected to the direct current biasing voltage 109, the other terminal is connected to the grid of an intermediate amplifier tube through the medium of a radio-frequency choke 110. The primary of. each transformer is connected to one phase of, a 3- phase BOO-cycle supply. The choice of this. frequency is of importance in the operation of the system.

The output of the intermediate amplifier tube 102 is modulated to, say, 65 cycles, by means of modulator 111 and after amplification by the power amplifier tube 112 is transferred to the antennae 113and 114 through the inductive relations between the stator 115 and the rotors 116 and 117. Ina similar manner, the output of the intermediate amplifier tubes 103 and 104 is mode ulated to, say, 108.7 and 86.7 cycles, respectively, by means of modulators 118 and 119, amplified by power amplifiers 120 and 121 and transferred to the antennas 113 and 114 through the inductive relations of the stators 122 and 123 and the rotors 116 and 117.

The direct current biasing voltage applied to the grids of the intermediate-amplifier tubes is oi such magnitude that (in the absence of the three-phase SOD-cycle supply) no power is transtrv mitted through these tubesJ-" In series with common direct current biasing voltage, each grid circuit'hasinduced init one of the phase Voltages of the three-phase BOO-cycle supply. The resultant biasing voltages impressed on the grid of each of the three intermediate amplifying tubes is indicated by curves 124, 125 and 126, respective: ly, of Figure 5. Since EC is thelcutoif voltage, each tube passes power only during the-positive half-cycle of its alternating current biasing voltage. Asa result no two amplifier tubes transmitpower simultaneously except during the small intervals of time a-b, c-rt, etc. as" shown in Figure 5.-

" The proportion of power transmitted during these intervals is less than theratio of shaded area' cob to totalarea of transmission per cycle for one tube E0 ob, since the tube is then operating on the knee of'its characteristic curve. lhe

amount of coupling still present may be further reduced by increasing thecommondirectcurrent bias voltage, but this results also'in a decrease of total'power transmitted. In practice this fur ther reduction is unnecessary, the beacon performance proving satisfactory without it i Neglectingthe small-amount of coupling present,'the beacon space pattern becomes as shown in Figure 6, in which 12'7fdenotes the radiation intensity of the'carrier and side bands modulated at '65 cycles from stator 115,128 and 129 denote similar characteristics, modulated at 108.3 and 86.7 cycles, respectively, from the stators 122 and K Note that' since but onestator winding is excited atla time, there are three independent carapproximately 20 cycles to any of the harmonics of the modulation frequencies used in the beacon. To illustrate the reason for this requirement assume thata frequency of 262 cycles were chosen for the three-phase alternator, The fourth harmonic of 65 cycles and the third harmonic of 36 cycles are each 250 cycles. ,Under this condition a beating of the reed indicator at the difierence frequency of 2 cycles is obtained.

The same means are available for shifting the beacon courses from their degree space relationship (in order to align them with the airways emanating from a given airport) as has been previously employed in connection with the fourcourse beacon. A simpler method applicable only to the 12-course beacon. is, however, preferable. This method consists of displacing the stator windings from their normal 120 degree positions. c

Since the stators are excited one at a time, displacementv of a given stator results in an equivalent displacement of the field pattern due to that stator. Thus, Figure 8 is the received'polar pattern when stator 122 is displaced by 20 degrees from its normal position. The pattern due to'122 is similarly displaced. The eight courses formed by the intersection-of the pattern due to stator 122, with the patterns this (Compare with Figure fl.) v

due to 115 and'123 are all shifted by 10 degrees in the direction of displacement'of 122 while the four courses due to the patterns of 115 and 123 remain fixed in their normal positions. A greater variation ofthe angles between courses may be obtained by displacing two of the three stators in equal amounts, but in opposite directions.

7 Using this method of attack, it becomes possible to align the beacon courses with the airways at a great number of airports. In certain special cases, however, it may become necessary to resort to other methods or course shifting already known to the art. i 7 What I claim is: 7 1. A method 'for producing adirective radio beacon providing more than four beacon courses, which includes generating more than two -modulated waves having the same carrier frequency but each modulated by'a diiferen't selected audiofrequency modulation signal, interrupting said modulated' waves so that they occur singly at suc- 'cessive intervalsof time, adjusting the rate of interruption so that eachof said modulation sig-' nals are'continuous in efiect upon receptiomand combining saidfinterrupted modulated waves ina pair of directional radiation sources so that the resultant radiateduwaves contain figure-of-eight space patterns corresponding to each of said mod ulated waves,'theaxes of said space patterns intersecting at predetermined angles with each other. i I

2. Atransmitterand antenna system comprising two loop antenna arranged at right angles toeach other, a source ofradio-frequency carrier, three amplifying branches each provided with one or more amplifying tubes, an automatic switching circuit for exciting one amplifier branch at a time by means of a multi-phase alternating current supply in series with a common direct current biasing voltage, each grid circuit having induced in it one ofthe phase'voltages of the multi-phase alternating current supply;

3.-In abeacon transmitter, the combination with means for producing in rapid successionfor varying said transfer means whereby the enof their inductive relationship with the secondary windings is exactly neutralized.

5. In a beacon transmitter, the combination with a source of radio frequency energy, of three amplifying branches for amplifying said radio frequency energy, three equivalent tuned circuit loads fed by said amplifying branches, and means for rapidly switching said radio-frequency energy successively to each of said tuned loads comprising a source of three-phase substantially low frequency, alternating voltage and a source of negative direct voltage applied to the input circuit I of each of saidamplifying branches in series with one of the phase voltages of said three-phase alternating voltage whereby each of said power amplifying branches passes said radio frequency energy only during a portion of the positive halfcycle of the alternating low-frequency voltage applied to its input circuit.

6. In a beacon transmitter, the combination with means for producing a plurality of modulated waves each of the same carrier frequency but having a selected modulation frequency differing from each of the other waves, of means for suppressing said carrier frequency in each of said modulated waves, means for transferring the resultant sets of side band frequencies to two directive antenna whereby said sets of side band waves are transmitted in predetermined direc-' tions, means for radiating in all directions a carrier wave of identical frequency with the suppressed carriers and of proper phase to combine with said sets of side band waves to produce a multi-course radio beacon space pattern and means for varying the directions of transmission of said side band waves whereby said beacon space pattern may be rotated in space or fixed at any desired orientation. l V

7. A goniometer comprising three primary windings placed at predetermined angles to each other, meansfor electrically shielding said primary windings fromeach other, two secondary windings crossed at right angles and each in mutual inductive relationship with all of said primary windings, and means. for rotating said secondary windings with respect to said primary windings whereby the mutual inductance between each of said secondary windings and each of said primary windings is varied .in su stantially sinusoidal relation.

8. In a beacon transmitter, the combination with a source of radio'frequency energy, of a plurality of amplifying branches for amplifying said radio frequency energy, two directive antenna crossed at right angles, and a goniometer comprising more thatn two primary windings placed at predetermined angles to each other and each fed froma corresponding one'of said amplifying branches, said primarywindings being in mutual inductive relationship with two ,mutually perpendicular secondary windings each of whic is connected to one of said directive an tennw, whereby the same radiated space pattern may be produced as from a system of directive antennae equal to in number and placed in the same angular relationship as said primary windings of said goniometer and coupled directly each to a' corresponding one of said amplifying branches.

9. A method for producing a multi-course directive radio beacon which comprises transmitting simultaneously in definite directions a plurality of radio frequency fields each with a different selected audio-frequency modulation and from each of which the carrier frequency has been suppressed and resupplying the carrier wave in proper time phase relationship by radiation from a non-directional antenna.

10. A goniometer comprising three primary windings located in separate shielded compartments and placed at predetermined angles to each other, two secondary windings crossedat right angIeaeachoi said secondary windings con.-

' sisting of three separate sections in mutual inductiverclationshipwith corresponding ones of said primary windings, and means of intercoupling said primary windings whereby the indirect coupling between said windings by virtue of their inductive relationship with said secondary windings is exactly neutralized.

' 11. A goniometer comprising three primary windings located in separate shielded compartments and placed at predetermined angles to each other, two secondary windings crossed at right angles, each of said secondary windings consisting of three separate sections in mutual inductive relationship with corresponding ones of said primary windings, and meansjfor, rotating said secondary windings with respect to said primary windings whereby the mutual inductance between each of said secondary windings and each of said primary windings is varied in substantially sinusoidal relation. V

a HARRY DIAMOND. 

